1. Field of the Invention
The present invention relates to a leadframe included in a resin-sealed semiconductor device.
2. Description of the Background Art
When a resin-sealed semiconductor device, for example, is fabricated, a leadframe is prepared to mount a semiconductor element (chip) thereon.
FIG. 18 is a perspective view showing a configuration of a background-art leadframe 100. A metal sheet is processed to form the leadframe 100. The leadframe 100 has a pad 2 for mounting the semiconductor element 3 at its center portion, which is supported by suspension leads 6a to 6d from four directions. Inner leads 5 radially extend from the periphery towards the pad 2. The inner leads 5 are connected to electrode portions of the semiconductor element 3 with metal thin wires 4.
After the leadframe 100 in the state of FIG. 18 is obtained, the semiconductor element 3 is sealed in resin such as epoxy resin and the inner leads 5 and the suspension leads 6a to 6d are cut off from the leadframe 100.
In a case of a semiconductor package which includes a larger number of inner leads 5, such as a multiple pin QFP (Quad Flat Package), each inner lead 5 becomes narrower and longer and its rigidity becomes lower. To prevent deformation of such inner lead 5 in a fabricating process, a support tape is applied to the inner leads 5 and the suspension leads 6a to 6d. As to the support tape, a variety of forms are proposed as below.
FIG. 18 shows a rectangular ring-shaped support tape 201. The rectangular ring-shaped support tape 201 is applied to the inner leads 5 and the suspension leads 6a to 6d around the pad 2. Since the support tape is rectangular, the inner leads 5 and the suspension leads 6a to 6d are not deformed or displaced even if the support tape 201 contracts.
FIG. 19 is a plan view illustrating a manner of taking the support tape 201 out of its material. The material 200 for the support tape 201 is generally supplied in tape form, and a rectangular ring-shaped support tape 201 is punched and applied to the inner leads 5. In this case, there are remaining portions 202 and 203, and the material 200 is disadvantageously utilized with low efficiency. In general, the material 200 is expensive, and therefore inefficient use of the material 200 leads to a costly leadframe 100.
To solve the problem of the structure of FIG. 18, use of strip-shaped support tapes, instead of rectangular ring-shaped support tapes, is proposed. FIG. 20A is a plan view showing a configuration of a leadframe 101 and FIG. 20B is a section taken along the line 20B--20B and viewed from the direction of the arrow of FIG. 20A.
The support tapes 211 and 221 are of strip-shape and applied to all of the inner leads and suspension leads 6a to 6d. FIG. 21 is a plan view illustrating a manner of taking the support tapes 211 and 221 out of their materials 210 and 220 in tape form. The support tapes 211 and 221 can be taken out of the materials 210 and 220 with higher efficiency than in the structure of FIG. 18 since those support tapes are rectangular.
With this type of support tapes, however, the inner leads 5 are deformed at the suspension leads 6a to 6d and their vicinities, e.g., in an area A including the suspension lead 6b and its vicinity. FIG. 22 is an enlarged plan view of an area A and its vicinity of FIG. 20A. Among the inner leads 5, an inner lead 501 adjacent to the suspension lead 6b to which both the support tapes 211 and 221 are applied is pulled in the directions of the arrows by contractions of the support tapes 211 and 221. The inner lead 501 is thereby deformed and comes into contact with an adjacent inner lead 502 at a point B. Then, the suspension lead 6b and the inner lead 502 are also deformed.
To solve the problems of the structure of FIGS. 18 and 20A, it is also proposed that the strip-shaped support tapes 211 and 221 should be applied to the inner leads 5 and the suspension leads 6a to 6d with their end portions overlapped. FIG. 23A is plan view showing a configuration of a leadframe 102 and FIG. 23B is a section taken along the line 23B--23B of FIG. 23A and viewed from the direction of the arrow.
The end portions of the strip-shaped support tapes 211 and 221 are overlapped to form a rectangular ring-shaped support tape on the whole and further their materials 210 and 220 can be utilized with higher efficiency. Moreover, at their overlapped end portions, stresses generated by contraction along the directions of the respective lengths of the support tapes 211 and 221 are balanced and the suspension leads 6a to 6d are given stresses only in a direction towards the pad 2. That avoids deformation of the suspension leads 6a to 6b.
It is not desirable, however, that many portions are each given stresses in different directions at an angle of 90.degree. when the support tapes contract. The reason is the alignment of their end portions to be overlapped should be accurately made in order to balance the stresses applied to the support tapes 211 and 221 along the directions of their lengths.